Figure 7.

Studying metabolic flux by use of labeled inputs. Glycolytic and TCA cycle analytes are particularly amenable to labeling of initial metabolite pools using stable isotopes (e.g., ¹³C glucose or acetate) and subsequent monitoring of intermediates and bottlenecks in those subsystems. Other similar opportunities exist as well; fatty acid incorporation into lipids, ¹⁵N labeling of nucleotide precursors of deoxynucleotides, and bioorthogonal approaches are all examples. Cells with increased glutaminase activity can be identified by supplementation of isotopically labeled glutamine during introduction into the TCA cycle. Dang et al.⁹² monitored TCA cycle metabolites to functionally characterize R132H mutation to isocitrate dehydrogenase in gliomas. The product, D-2-hydroxyglutarate, has been implicated as affecting oncogenic transformation although its precise role is as yet undefined^97,98.